DETROIT — Billions of dollars in government loans to prop up General Motors and Chrysler won't be enough. The companies, which have received $17.4 billion so far, filed plans with the government more than doubling that request to a staggering total of $39 billion.

The requests, made in government-required restructuring plans filed Tuesday, were accompanied by plans for thousands more job cuts, slashing of models and brands, union concessions and the prospect of even further expense cuts.

In a dramatic acknowledgment that conditions in the U.S. auto industry have grown significantly worse in just two months, GM alone said it would cut 47,000 jobs globally by the end of the year — 19 percent of its work force. It also said it would close five more U.S. factories, though it did not identify them.

Chrysler said it will cut 3,000 more jobs and stop producing three vehicle models.

The grim reports came as the United Auto Workers union said it had reached a tentative agreement with GM, Chrysler and Ford Motor Co. on contract changes. Concessions with the union and debt-holders were a condition of the government bailout.

GM said it could need up to $30 billion from the Treasury Department, up from a previous estimate of $18 billion. That includes $13.4 billion the company has already received. The world's largest automaker said it could run out of money by March without new funds and needs $2 billion next month and another $2.6 billion in April.

"We have a lot of work to do," General Motors Corp. Chairman and Chief Executive Rick Wagoner said. "We're still going at this with a great sense of urgency."

GM's request includes a credit line of $7.5 billion to be used if the downturn is more pronounced than expected. But the automaker claimed it could be profitable in two years and repay its loans by 2017.

The requests pale in comparison to what it might cost taxpayers if GM or Chrysler go bankrupt, said Aaron Bragman, auto industry analyst for the consulting firm IHS Global Insight in Troy, Mich.

"These are not small, insignificant organizations," he said. "These are the lifeblood of American manufacturing."

The company looked into three bankruptcy scenarios, all of which would cost the government more than $30 billion, GM Chief Operating Officer Fritz Henderson said.

Although little is known about whether people would buy cars from a bankrupt automaker, some research "suggests that sales fall off a cliff," Henderson said.

Chrysler LLC requested $5 billion in new loans on top of $4 billion it received in December. That's $2 billion more than expected.

Both requests were part of restructuring plans the two automakers owed the government in exchange for earlier loans.